A deeper insight into the characteristics of double-layer oil-in-water emulsions stabilized by Persian gum and whey protein isolate

In situ single-droplet analysis of emulsified fat using confocal Raman microscopy: insights into crystal network formation within spatial resolution

Fat crystallization is one of the predominant factors influencing the structure and properties of fat-containing emulsions. In the present study, the role of emulsifiers on fat crystallization dynamics within droplet multiphase systems was evaluated via single-droplet analysis, taking advantage of the non-destructive properties of confocal Raman microscopy. Palm oil droplets dispersed in water were used as a model system, due to palm oil's well-known crystallization properties. Emulsion droplets of the same size were generated using two different emulsifiers (Whey Protein Isolate and Tween 60), at various concentrations. Fast and slow cooling treatments were applied to affect fat crystallisation and network formation as well as droplet morphology, and crystallization dynamics. Raman imaging analysis demonstrated that the chemical structure and concentration of the emulsifier significantly influenced both crystal nucleation within the droplets, as well as the spatial distribution and morphology of the fat crystal network. Additionally, analysis of the spectra of the crystallized phase provided essential information regarding the impact of the emulsifiers on the microstructure, degree of structural order, and structural arrangements of the fat crystal networks. Furthermore, by performing single droplet analysis during cooling it was possible to observe shape distortions in Tween 60 stabilized droplets, as a consequence of the formation of a three-dimensional network of fat crystals that strongly interacted with the interface. On the other hand, the droplets retained their shape when whey proteins were absorbed at the interface. Confocal Raman microscopy, in combination with polarized light microscopy, is, therefore, a well-suited tool for in situ, single-droplet analysis of emulsified oil systems, providing essential information about emulsified fat crystallization dynamics, contributing to better understanding and designing products with enhanced structure and function.

Novel Pickering emulsion stabilized by glycosylated whey protein isolate: Characterization, stability, and curcumin bioaccessibility

Pickering emulsions prepared from protein-polysaccharide complexes have attracted increasing attention. In this study, whey protein isolates (WPI) were modified with oligochitosan using transglutaminase (TGase)-type to fabricate Pickering emulsions, and loaded with curcumin. The curcumin/protein ratio of 1:25 and oil phase fraction (φ = 17 %) are the most optimal condition for emulsions stabilization, and particle size of glycosylated WPI emulsion was 31.70 μm. Glycosylated WPI emulsion had the highest encapsulation efficiency (96.64 %) of curcumin. Microstructure analysis showed that glycosylated WPI had small droplets covered by dense interface layers. The modified WPI emulsions exhibited optimal emulsifying properties and emulsion stability, which effectively inhibited the premature water-oil stratification in emulsion. In vitro digestion results showed that WPI-oligochitosan complexes enhanced curcumin bioaccessibility (40.34 %). The antioxidant activity of glycosylated WPI emulsions was significantly increased. The results of this study provide helpful references for applying glycosylated WPI-stabilized Pickering emulsions, which can be used as transport carriers of curcumin.

Improving the physicochemical stability of Pickering emulsion stabilized by glycosylated whey protein isolate/cyanidin-3-glucoside to deliver curcumin

Protein-polysaccharide-polyphenol delivery systems function as a promising tool to deliver bioactive ingredients aiming to improve their solubility and bioavailability. In this study, whey protein isolate (WPI), short-chain inulin (SCI), and cyanidin-3-glucoside (C3G) were first used to stabilize Pickering emulsions. The physicochemical properties and stability of curcumin encapsulated or not in Pickering emulsions were explored. Results showed that glycosylation and C3G reduced surface and interfacial tension on protein surfaces and inhibited the aggregation of emulsion droplets, thereby reducing the emulsion's particle size. WPI-SCI/C3G stabilized Pickering emulsion had the best stability. The CLSM results showed that the WPI-SCI and WPI-SCI/C3G stabilized emulsions were uniformly dispersed, suggesting that glycosylation and the interaction between protein and C3G enhanced the adsorption capacity of the interfacial protein and improved the stability of the Pickering emulsion. The retention rates of curcumin-loaded WPI-SCI- (67.34 %) and WPI-SCI/C3G- (77.07 %) stabilized Pickering emulsions on day 8 of storage were higher than those in WPI- (33.97 %) and WPI/C3G- (37.02 %) stabilized emulsions, and the degradation half-life was also extended from 7 days to >15 days. These findings provide a theoretical basis for the application of WPI Pickering emulsion and indicate a useful means for the delivery of bioactive components.

Characterization and stability of peppermint oil emulsions using polyglycerol esters of fatty acids and milk proteins as emulsifiers

Three peppermint oil emulsions using polyglycerol esters of fatty acids-casein (PGFE-CN), polyglycerol esters of fatty acids-sodium caseinate (PGFE-NaCN), and polyglycerol esters of fatty acids-whey protein isolate (PGFE-WPI) as emulsifiers were fabricated, and the droplet size, zeta potential, viscosity, and stability of emulsions were determined. The experimental results showed that the emulsion containing PGFE-CN has relatively smaller droplet size of 231.77 ± 0.49 nm. No significant changes were observed on the average particle size, polydispersity index and zeta potential during 4-week of storage, indicating that the emulsions kept stable against pH, salt ion, freeze-thaw, and storage. Fourier transform infrared spectrometer (FTIR) results showed that the electrostatic interaction occurs between CN and PGFE in the emulsion. The confocal laser scanning microscope (CLSM) was used to observe the microstructure of the emulsion, proving that droplets were evenly distributed throughout the aqueous phase by PGFE-CN emulsifier. The protein-stabilized emulsions can be used as potential carriers for the delivery of the lipophilic nutrients such as peppermint oil. PRACTICAL APPLICATION: PGFE-CN emulsifier can be directly added to the beverage systems containing oil or protein, such as coconut milk, peanut milk, and walnut milk. It can enhance the stability of beverage, prevent the precipitation, stratification, and oil floating, improve the homogeneity of the system and therefore extend the shelf life.